Optical Tube Assembly Having a Dry Insert and Methods of Making the Same

ABSTRACT

An optical tube assembly having at least one optical waveguide, at least one dry insert, and a tube. The at least one optical waveguide is disposed within the tube and generally surrounds the at least one optical waveguide. In one embodiment, the dry insert has a first layer comprising a felt having at least one type of non-continuous filament. The dry insert may also include a plurality of water-swellable filaments. In another embodiment, a dry insert has a first layer, a second layer, and a plurality of water-swellable filaments. The first and second layers are attached together at least along the longitudinal edges thereof, thereby forming at least one compartment between the first and second layers and the plurality of water-swellable filaments are generally disposed in the at least one compartment. The dry insert also is advantageous in tubeless cable designs.

RELATED APPLICATIONS

The present application is a Divisional of U.S. Ser. No. 11/881,280filed on Jul. 26, 2007, which is a Continuation-In-Part of U.S. Ser. No.10/661,204 filed on Sep. 12, 2003, now U.S. Pat. No. 7,336,873, which isa Continuation-In-Part of U.S. Ser. No. 10/326,022 filed on Dec. 19,2002, now U.S. Pat. No. 6,970,629, the disclosures of which areincorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates generally to dry packaging of opticalwaveguides. More specifically, the invention relates to an optical tubeassembly that includes at least one dry insert for protecting at leastone optical waveguide.

BACKGROUND

Fiber optic cables include optical waveguides such as optical fibersthat transmit optical signals, for example, voice, video, and/or datainformation. One type of fiber optic cable configuration includes anoptical waveguide disposed within a tube, thereby forming a tubeassembly. Generally speaking, the tube protects the optical waveguide;however, the optical waveguide must be further protected within thetube. For instance, the optical waveguide should have some relativemovement between the optical waveguide and the tube to accommodatebending. On the other hand, the optical waveguide should be adequatelycoupled with the tube, thereby inhibiting the optical waveguide frombeing displaced within the tube when, for example, pulling forces areapplied to install the cable. Additionally, the tube assembly shouldinhibit the migration of water therein. Moreover, the tube assemblyshould be able to operate over a range of temperatures without undueoptical performance degradation.

Conventional optical tube assemblies meet these requirements by fillingthe tube with a thixotropic material such as grease. Thixotropicmaterials generally allow for adequate movement between the opticalwaveguide and the tube, cushioning, and coupling of the opticalwaveguide. Additionally, thixotropic materials are effective forblocking the migration of water within the tube. However, thethixotropic material must be cleaned from the optical waveguide beforeconnectorization of the same. Cleaning the thixotropic material from theoptical waveguide is a messy and time-consuming process. Moreover, theviscosity of thixotropic materials is generally temperature dependent.Due to changing viscosity, the thixotropic materials can drip from anend of the tube at relatively high temperatures and the thixotropicmaterials may cause optical attenuation at relatively low temperatures.

Cable designs have attempted to eliminate thixotropic materials from thetube, but the designs are generally inadequate because they do not meetall of the requirements and/or are expensive to manufacture. One examplethat eliminates the thixotropic material from the tube is U.S. Pat. No.4,909,592, which discloses a tube having conventional water-swellabletapes and/or yarns disposed therein. For instance, conventionalwater-swellable tapes are typically formed from two thin non-wovenlayers that sandwich a water-swellable powder therebetween, therebyforming a relatively thin tape that does not fill the space inside abuffer tube. Consequently, conventional water-swellable tapes do notprovide adequate coupling for the optical waveguides because of theunfilled space. Additionally, the space allows water within the tube tomigrate along the tube, rather than be contained by the conventionalwater-swellable tape. Thus, this design requires a large number ofwater-swellable components within the tube for adequately coupling theoptical fibers with the tube. Moreover, the use of large numbers ofwater-swellable components inside a buffer tube is not economicalbecause it increases the manufacturing complexity along with the cost ofthe cable.

Another example that eliminates the thixotropic material from a fiberoptic cable is U.S. Pat. No. 6,278,826, which discloses a foam having amoisture content greater than zero that is loaded with super-absorbentpolymers. The moisture content of the foam is described as improving theflame-retardant characteristics of the foam. Likewise, the foam of thisdesign is relatively expensive and increases the cost of the cable.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of a tube assembly according to thepresent invention.

FIG. 1 a is a cross-sectional view of another tube assembly according tothe present invention.

FIG. 2 is a cross-sectional view of the dry insert of the tube assemblyof FIG. 1.

FIG. 2 a is a cross-sectional view of another dry insert according tothe present invention.

FIGS. 2 b-2 d depict various configurations of an adhesive/glue appliedto the dry insert of FIG. 2.

FIGS. 3 and 3 a are cross-sectional views of tube assemblies accordingto the present invention having the dry insert of FIG. 2 a.

FIG. 4 is a schematic representation of a manufacturing line accordingto the present invention.

FIG. 5 is a cross-sectional view of a fiber optic cable according to thepresent invention using the tube assembly of FIG. 1.

FIG. 6 is a cross-sectional view of a fiber optic cable according to thepresent invention using the tube assembly of FIG. 3.

FIG. 7 is a perspective view of another dry insert according to theconcepts of the present invention.

FIG. 8 is a cross-sectional view of another dry insert according to theconcepts of the present invention.

FIG. 9 is a perspective view of another dry insert according to theconcepts of the present invention.

FIG. 10 is a perspective view of another dry insert according to theconcepts of the present invention.

FIG. 11 is a cross-sectional view of a fiber optic cable having aconventional grease filled tube assembly.

FIG. 12 is a cross-sectional view of a fiber optic cable having aconventional dry tube assembly.

FIG. 13 is a cross-sectional view of a fiber optic cable with an armorlayer according to the present invention.

FIG. 14 is a cross-sectional view of a tubeless fiber optic cableaccording to the present invention.

FIG. 15 is a cross-sectional view of a fiber optic cable having strandedtubes according to the present invention.

FIG. 16 is a cross-sectional view of the dry insert of FIG. 2 a havingan additional layer.

FIG. 17 is a cross-sectional view of still another embodiment of the dryinsert according to the present invention.

FIG. 18 is a plan view of the dry insert of FIG. 17.

FIGS. 19 and 20 are cross-sectional views of tubeless fiber optic cablesaccording to the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings showing preferred embodiments ofthe invention. The invention may, however, be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein; rather, these embodiments are provided so that thedisclosure will fully convey the scope of the invention to those skilledin the art. The drawings are not necessarily drawn to scale but areconfigured to clearly illustrate the invention.

Illustrated in FIG. 1 is an exemplary tube assembly 10 according to oneaspect of the present invention. Tube assembly 10 includes at least oneoptical waveguide 12, at least one dry insert 14, and a tube 18. In thiscase, the at least one optical waveguide 12 is in the form of a stack ofribbons 13 having a diagonal D dimension across the corners of thestack. Dry insert 14 generally surrounds the at least one opticalwaveguide 12 and forms core 15, which is disposed within tube 18. Dryinsert 14 performs functions such as cushioning, coupling, inhibitingthe migration of water, and accommodates bending. Dry insert 14 isadvantageous because the optical waveguides are easily removed therefromwithout leaving a residue or film that requires cleaning beforeconnectorization. Moreover, unlike conventional thixotropic materials,dry insert 14 does not change viscosity with temperature variations orhave a propensity to drip from an end of the tube at high temperatures.Furthermore, tube assembly 10 can include other suitable components suchas a polyester binder thread 17 to hold dry insert 14 about opticalwaveguide 12. Likewise, two or more threads may be stitched together forholding dry insert 14 together before extruding tube 18 therearound.FIG. 1 a shows tube assembly 10′, which is a variation of tube assembly10. Specifically, tube assembly 10′ includes a plurality of looseoptical waveguides 12, instead of the stack of ribbons 13. In this case,tube assembly 10′ includes twenty-four loose optical waveguides 12having diagonal dimension D, but any suitable number of opticalwaveguides may be used. Moreover, optical waveguides 12 may be bundledinto one or more groups using binders, water-swellable threads, tapes,wraps, or other suitable materials. Additionally, tube assemblies 10 or10′ can be a portion of cable as shown in FIG. 5. Furthermore, dryinserts 14 according to the present invention may be used with tubelesscable designs.

As depicted, optical waveguide 12 is an optical fiber that forms aportion of an optical fiber ribbon. In this case, the optical waveguidesare a plurality of single-mode optical fibers in a ribbon format thatform ribbon stack 13. Ribbon stack 13 can include helical or S-Zstranding. Additionally, other types or configurations of opticalwaveguides can be used. For example, optical waveguide 12 can bemulti-mode, pure-mode, erbium doped, polarization-maintaining fiber,other suitable types of light waveguides, and/or combinations thereof.Moreover, optical waveguide 12 can be loose or in bundles. Each opticalwaveguide 12 may include a silica-based core that is operative totransmit light and is surrounded by a silica-based cladding having alower index of refraction than the core. Additionally, one or morecoatings can be applied to optical waveguide 12. For example, a softprimary coating surrounds the cladding, and a relatively rigid secondarycoating surrounds the primary coating. In one embodiment, one or moreoptical waveguides 12 include a coating system as disclosed in U.S.patent application Ser. No. 10/632,219 filed on Jul. 18, 2003, thedisclosure of which is incorporated herein by reference. Opticalwaveguide 12 can also include an identifying means such as ink or othersuitable indicia for identification. Suitable optical fibers arecommercially available from Corning Incorporated of Corning, N.Y.

In other embodiments, ribbon stack 13 can have a corner opticalwaveguide(s) 12 a with a predetermined MAC number, thereby inhibitingoptical attenuation of the corner optical waveguide when subjected tocompressive forces. Stated another way, selecting corner opticalwaveguides with a predetermined MAC number places optical waveguidesthat are less sensitive to optical attenuation from compressive forcesin ribbon stack locations that experience relatively high levels ofcompression. As used herein, MAC number is calculated as a mode fielddiameter (MFD) divided by a cutoff wavelength for the given opticalwaveguide 12 a where both quantities are expressed in micrometers sothat the MAC number is dimensionless. In other words, MFD is typicallyexpressed in micrometers and cutoff wavelength is typically expressed innanometers, so the cutoff wavelength must be divided by 1000 to convertit to micrometers, thereby yielding a dimensionless MAC number.

In one embodiment, one or more of the corner optical waveguides 12 ahave a predetermined MAC number. Specifically, the MAC number is about7.35 or less, more preferably about 7.00 or less, and most preferablyabout 6.85 or less. By way of example, corner optical waveguide(s) 12 ais selected with a MFD of 9.11 μm or less and a cutoff wavelength of1240 nm or more, thereby yielding 7.35 or less for the MAC number.Generally speaking, the MAC number is directly proportional to MFD andinversely proportional to the cutoff wavelength. Ribbon stack 13 hasfour corner optical waveguides 12 a; however, other ribbon stackconfigurations can include more corner positions. For instance, a ribbonstack having a generally plus sign shape includes eight outer corners.Likewise, other ribbon stack configurations may have other numbers ofcorner positions.

Additionally, ribbon embodiments of the present invention may have apositive excess ribbon length (ERL), although a negative ERL ispossible. As used herein, ERL is defined as the length of the particularribbon minus the length of the tube or cable containing the ribbondivided by the length of the tube or cable containing the ribbon, whichcan be expressed as a percentage by multiplying by 100. Whether the ERLis calculated using the tube length or the cable length depends on theparticular configuration. Moreover, individual ribbons of a cable canhave different values of ERL. By way of example, ribbons of the cablehave a positive ERL, preferably a positive ERL in the range of about0.0% to about 0.2% or greater. Likewise, embodiments having loose orbundled optical fibers may include a positive excess fiber length (EFL).

FIGS. 2 and 2 a illustrate cross-sectional views of explanatory dryinserts 14 according to the present invention. Dry inserts 14 are formedfrom an elongate material or materials that are capable of being paidoff from a reel for a continuous application during manufacture. Dryinserts 14 may be formed from a plurality of layers (FIG. 2) that canperform different functions; however, dry insert 14 (FIG. 2 a) can alsobe a single layer such as a felt material that is compressible. Dryinsert 14 cushions optical waveguide 12 from tube 18, therebymaintaining optical attenuation of optical waveguide 12 below about 0.4dB/km at a reference wavelength of 1310 nm and 0.3 dB/km at a referencewavelengths of 1550 nm and 1625 nm. In one embodiment, dry insert 14 isformed from two distinct layers and/or materials. For instance, FIG. 2depicts a first layer 14 a of dry insert 14 that is a compressible layerand second layer 14 b that is a water-swellable layer. In this case,first layer 14 a is formed from a compressible material having apredetermined spring constant for providing adequate couplingcharacteristics. By way of example, the first layer is a foam tape,preferably, an open cell foam tape; however, any suitable compressiblematerial can be used such as a closed cell foam tape. Second layer 14 bis a water-swellable layer such as a tape having a water-swellablepowder that inhibits the migration of water within tube 18.Additionally, single layer dry inserts according to the presentinvention can have similar characteristics.

FIG. 2 a depicts another dry insert 14 having a single, non-woven layerof felt made of one or more materials. In this case, dry insert 14comprises a plurality of water-swellable filaments 24 a along with otherfilaments 24 b that are non-swellable in water, thereby forming a layerof felt having multiple materials. As used herein, felt means a materialcomprising one or more types of non-continuous filaments and/or fiberswhich have been caused to adhere and mat together through the action ofheat, moisture, chemicals, pressure, or a combination of the foregoingactions, thereby forming a relatively thick and compressible layer.Water-swellable filaments 24 a may comprise any suitable water-swellablematerial, but preferably include at least one superabsorbant polymer.Preferred superabsorbent polymers are partially cross-linked polymersthat absorb many times their own weight in water and swell considerablywithout dissolving, for example, acrylate, urethane or cellulosic-basedmaterials. By way of example, the single layer dry insert 14 of FIG. 2 amay include about 25% or less by weight of water-swellable filaments 24a and about 75% or more by weight of other filaments 24 b; however,other suitable ratios are possible. Likewise, in this configuration thedensity of the dry insert can be influenced to meet the needs of thetube assembly. Generally speaking, the single layer felt dry insert is acompressible layer for cushioning and coupling of the optical fibers andmay include water-swellable materials for inhibiting the migration ofwater. Unlike conventional water-swellable tapes the single layer felthas a relatively large thickness that generally speaking fills spaceswithin the tube or cavity. Moreover, the felt dry insert may usewater-swellable filaments that aid in providing compressibility orfluffyness of the dry insert, rather than water-swellable powders thatare used in conventional water-swellable tapes.

Other filaments 24 b may include any suitable filament and/or fibermaterial such as polymer filaments like polypropylene, polyethylene, andpolyesters, likewise, other suitable materials such as cottons, nylon,rayons, elastomers, fiberglass, aramids, polymers, rubber-basedurethanes, composite materials and/or blends thereof may be included asa portion of other filaments 24 b and may be tailored for providingspecific characteristics. For instance, polymer filaments can be usedfor coupling the dry insert with the tube when the same is extrudedthereover. In other words, the hot tube extrudate at least partiallymelts the polymer filaments, thereby causing adhesion between the two.Another example is that elastomeric fibers can be included in the dryinsert for providing improved coupling of optical waveguide 12 with tube18. The use of elastomeric fibers, or other suitable material, may allowfor the coupling of dry insert 14 to tube 18, and/or optical waveguide12 to dry insert 14 by increasing a coefficient of friction. Of course,as depicted in FIGS. 2 b-2 d adhesives, glues, (FIGS. 2 b-2 d) or othermethods may be used for attaching the dry insert to the tube.Furthermore, the dry insert may include other chemicals or additives toinfluence properties such as flame-retardance.

FIGS. 3 and 3 a depict tube assemblies 30 and 30′ that are similar totube assemblies 10 and 10′ depicted in FIGS. 1 and 1 a, except theyemploy the dry insert of FIG. 2 a. Furthermore, tube assemblies 30 and30′ can be included as a portion of a fiber optic cable 60 as depictedin FIG. 6. Dry insert 14 of FIG. 2 a advantageously performs thefunctions of cushioning, coupling, inhibiting the migration of water,and accommodates bending like the multi-layer dry insert. Additionally,the single layer construction may reduce costs and improve cablemanufacturability.

Additionally, the dry insert of FIG. 2 a can include one or more otherlayers in addition to the felt for tailoring performancecharacteristics. Illustratively, FIG. 16 depicts another dry insert 14having a second layer 162 attached to one side of the felt dry insert ofFIG. 2 a. Using a second layer attached to the felt dry insert allowsfor several different dry insert configurations. For instance, the feltdry insert may exclude water-swellable filaments, and instead secondlayer 162 is a water-swellable tape that inhibits the migration ofwater. In another embodiment, the felt includes water-swellablefilaments and a water-swellable tape attached thereto. In a furtherembodiment, second layer 162 is a meltable layer having a polymer thatat least partially melts during extrusion of the tube thereover.Likewise, other dry insert embodiments are possible.

Illustratively, FIGS. 17 and 18 depict dry insert 14 having a first anda second layer 172,176 with at least one water-swellable layer 174disposed in a compartment 174 a therebetween. In other words,water-swellable layer 174 is generally contained in one or morecompartments 174 a between first and second layers 172,176 that act asbacking layers. By way of example, first and second layers may be formedof nylon, polymers, fiberglass, aramid, w-s tape, composite materials,or any other suitable materials in a tape-like configuration. Materialsfor this configuration should provide the necessary strength to endurethe cabling process and intended use. Additionally, at least one of thefirst and/or second layers should be porous for water penetration.Preferably, water-swellable layer 174 includes non-continuouswater-swellable filaments loosely disposed between first and secondlayers 172,174, thereby forming a compressible dry insert. Suitablewater-swellable filaments are, for example, LANSEAL materials availablefrom Toyobo of Osaka, Japan or OASIS materials available from TechnicalAbsorbents Ltd. of South Humberside, United Kingdom. Additionally,water-swellable layer 174 may comprise a water swellable powder alongwith the water swellable filaments. Moreover, water-swellable layer 174may include other filaments as a filler to increase the thickness of thewater swellable layer and thus of the dry insert, while reducing thecost of the dry insert. The other filaments may comprise any suitablenon-swellable as discussed herein.

Furthermore, first and second layers 172,176 are attached together sothat water-swellable layer 174 is generally sandwiched therebetween,thereby creating one or more compartments 174 a, which generallyspeaking traps water-swellable layer 174 therein. At a minimum, layers172,176 are attached together at a plurality of seams 178 along thelongitudinal edges, but are attachable in other ways. Layers 172,176 areattachable using adhesives, heat where appropriate, stitching, or othersuitable methods. In preferred embodiments, layers 172,176 are attachedat intermediate positions along the length of the dry insert. As shownin FIG. 18, layers 172,176 are attached together using a diamond patternof seams 178; however, other suitable patterns such as triangular,semi-circular, or curvilinear patterns are possible, thereby creatingthe plurality of compartments 174 a. Additionally, the seams betweencompartments can be arranged for aiding in forming the dry insert aboutthe optical waveguides. Compartmentalization of water-swellable layer174 advantageously inhibits moving or shifting of the material beyondthe individual compartment. Moreover, the compartments add a pillowlytexture to the dry insert.

In further embodiments, first and second layers 172,176 need notcomprise the same material. In other words, the materials of the firstand second layers may be selected to tailor the dry insert behavioraccording to the needs of each side of the dry insert. For instance, thefirst layer is tailored to adhere with the extruded tube and the secondlayer is tailored to have a smooth finish for contact with the opticalwaveguides. Additionally, in other embodiments the dry insert can havemore than a first and second layers to, for instance, optimize theattachment of the layers, coupling, and/or inhibit water migration.However, the dry insert should not be so stiff that it is too difficultto manufacture into a cable assembly. Additionally, as shown in FIG. 2 ait may be advantageous for one of the longitudinal edges of any of thedry inserts to have a tapered edges 24 c so that the longitudinal edgesmay overlap without a large bulge when the dry insert is formed aboutthe at least on optical fiber 12.

Dry inserts 14 of the present invention preferably have a water-swellspeed so that the majority of swell height of the water-swellablesubstance occurs within about 120 seconds or less of being exposed towater, more preferably about 90 seconds or less. Additionally, dryinserts 14 preferably has a maximum swell height of about 18 mm fordistilled water and about 8 mm for a 5% ionic water solution, i.e., saltwater; however, dry inserts with other suitable maximum swell heightsmay be used.

Dry inserts 14 may be compressed during assembly so that it provides apredetermined normal force that inhibits optical waveguide 12 from beingeasily displaced longitudinally along tube 18. Dry inserts 14 preferablyhave an uncompressed height h of about 5 mm or less for minimizing thetube diameter and/or cable diameter; however, any suitable height h canbe used for dry inserts 14. By way of example, a single layer dry insert14 can have an uncompressed height in the range of about 0.5 mm to about2 mm, thereby resulting in a tube assembly having a relatively smalldiameter. Moreover, height h of dry insert 14 need not be constantacross the width, but can vary, thereby conforming to thecross-sectional shape of the optical waveguides and providing improvedcushioning to improve optical performance (FIG. 10). Compression of dryinsert 14 is actually a localized maximum compression of dry insert 14.In the case of FIG. 1, the localized maximum compression of dry insert14 occurs at the corners of the ribbon stack across the diameter.Calculating the percentage of compression of dry insert 14 in FIG. 1requires knowing an inner diameter of tube 18, a diagonal D dimension ofthe ribbon stack, and an uncompressed height h of dry insert 14. By wayof example, inner diameter of tube 18 is 7.1 mm, diagonal D of theribbon stack is 5.1 mm, and the uncompressed height h of dry insert 14across a diameter is 3.0 mm (2 times 1.5 mm). Adding diagonal D (5.1 mm)and the uncompressed height h of dry insert 14 across the diameter (3.0mm) yields an uncompressed dimension of 8.1 mm. When placing the ribbonstack and dry insert 14 and into tube 18 with an inner diameter of 7.1mm, dry insert is compressed a total of 1 mm (8.1 mm-7.1 mm). Thus, dryinsert 14 is compressed by about thirty percent across the diameter oftube 18. According to the concepts of the present invention thecompression of dry insert 14 is preferably in the range of about 10% toabout 90%; however, other suitable ranges of compression may provide thedesired performance. Nonetheless, the compression of dry insert 14should not be so great as to cause undue optical attenuation in any ofthe optical waveguides.

In other embodiments, first layer 14 a of dry insert 14 is uncompressedin tube assembly 10, but begins to compress if optical waveguidemovement is initiated. Other variations include attaching, bonding, orotherwise coupling a portion of dry insert 14 to tube 18. For example,adhesives, glues, elastomers, and/or polymers 14 c are disposed on aportion of the surface of dry insert 14 that contacts tube 18 forattaching dry insert 14 to tube 18. Additionally, it is possible tohelically wrap dry insert 14 about optical waveguide 12, instead ofbeing longitudinally disposed. In still further embodiments, two or moredry inserts can be formed about one or more optical waveguides 12 suchas two halves placed within tube 18.

Other embodiments may include a fugitive glue/adhesive for couplingcable core 15 and/or dry insert 14 with tube 18. The glue/adhesive orthe like is applied to the radially outward surface of dry insert 14,for instance, during the manufacturing process. The fugitiveglue/adhesive is applied while hot or melted to the outer surface of dryinsert 14 and then is cooled or frozen when the cable is quenched orcools off. By way of example, a suitable fugitive glue is available fromNational Starch and Chemical Company of Bridgewater, N.J. under thetradename LITE-LOK® 70-003A. The fugitive glue or other suitableadhesive/material may be applied in beads having a continuous or anintermittent configuration as shown in FIGS. 2 b-2 d. For instance, oneor more adhesive/glue beads may be longitudinally applied along the dryinsert, longitudinally spaced apart beads, in a zig-zag bead along thelongitudinal axis of the dry insert, or in any other suitableconfiguration.

In one application, a plurality of beads of fugitive glue/adhesive orthe like is applied to dry insert 14. For instance, three continuous, ornon-continuous, beads can be disposed at locations so that when the dryinsert is formed about the ribbon stack the beads are about 120 degreesapart. Likewise, four beads can be disposed at locations so they areabout 90 degrees apart when the dry insert is formed about the opticalwaveguides. In embodiments having the beads spaced apart along thelongitudinal axis, the beads may have a longitudinal spacing S of about20 mm and about 800 mm or more; however, other suitable spacing may beused. Additionally, beads may be intermittently applied for minimizingthe amount of material required, thereby reducing manufacturing expensewhile still providing sufficient coupling/adhesion.

Since tube assemblies 10 are not filled with a thixotropic material thetube may deform or collapse, thereby forming an oval shaped tube insteadof a round tube. U.S. patent application Ser. No. 10/448,509 filed onMay 30, 2003, the disclosure of which is incorporated herein byreference, discusses dry tube assemblies where the tube is formed from abimodal polymeric material having a predetermined average ovality. Asused herein, ovality is the difference between a major diameter D1 and aminor diameter D2 of tube 18 divided by major diameter D1 and multipliedby a factor of one-hundred, thereby expressing ovality as a percentage.Bimodal polymeric materials include materials having at least a firstpolymer material having a relatively high molecular weight and a secondpolymer material having a relatively low molecular weight that aremanufactured in a dual reactor process. This dual reactor processprovides the desired material properties and should not be confused withsimple post reactor polymer blends that compromise the properties ofboth resins in the blend. In one embodiment, the tube has an averageovality of about 10 percent or less. By way of example, tube 18 isformed from a HDPE available from the Dow Chemical Company of Midland,Mich., under the tradename DGDA-2490 NT.

Coupling of the optical waveguide in the tube assembly may be measuredusing a normalized optical ribbon pullout force test. The ribbon pulloutforce test measures the force (N/m) required to initiate movement of aribbon stack from a 10-meter length of cable. Of course, this test isequally applicable to loose or bundled optical waveguides. Specifically,the test measures the force required to initiate movement of a stack ofribbons, or other configurations of optical waveguides, relative to thetube and the force is divided by the length of the cable, therebynormalizing the optical ribbon pullout force. Preferably, the ribbonpullout force is in the range of about 0.5 N/m and about 5.0 N/m, morepreferably, in the range of about 1 N/m to about 4 N/m.

FIG. 4 schematically illustrates an exemplary manufacturing line 40 fortube assembly 10 according to the present invention. Manufacturing line40 includes at least one optical waveguide payoff reel 41, a dry insertpayoff reel 42, an optional compression station 43, an glue/adhesivestation 43 a, a binding station 44, a cross-head extruder 45, a watertrough 46, and a take-up reel 49. Additionally, tube assembly 10 mayhave a sheath 20 therearound, thereby forming a cable 50 as illustratedin FIG. 5. Sheath 20 can include strength members 19 a and a jacket 19b, which can be manufactured on the same line as tube assembly 10 or ona second manufacturing line. The exemplary manufacturing processincludes paying-off at least one optical waveguide 12 and dry insert 14from respective reels 41 and 42. Only one payoff reel for opticalwaveguide 12 and dry insert 14 are shown for clarity; however, themanufacturing line can include any suitable number of payoff reels tomanufacture tube assemblies and cables according to the presentinvention. Next, dry insert 14 is compressed to a predetermined height hat compression station 43 and optionally an adhesive/glue is applied tothe outer surface of dry insert 14 at station 43 a. Then dry insert 14is generally positioned around optical waveguide 12 and if desired abinding station wraps or sews one or more binding threads around dryinsert 14, thereby forming core 15. Thereafter, core 15 is feed intocross-head extruder 45 where tube 18 is extruded about core 15, therebyforming tube assembly 10. Tube 18 is then quenched in water trough 46and then tube assembly 10 is wound onto take-up reel 49. As depicted inthe dashed box, if one manufacturing line is set-up to make cable 50,then strength members 19 a are paid-off reel 47 and positioned adjacentto tube 18, and jacket 19 b is extruded about strength members 19 a andtube 18 using cross-head extruder 48. Thereafter, cable 50 passes into asecond water trough 46 before being wound-up on take-up reel 49.Additionally, other cables and/or manufacturing lines according to theconcepts of the present invention are possible. For instance, cablesand/or manufacturing lines may include a water-swellable tape 19 cand/or an armor between tube 18 and strength members 19 a; however, theuse of other suitable cable components are possible.

Additionally, a ribbon coupling force test may be used for modeling theforces applied to the optical waveguide(s) when subjecting a cable to,for example, pulling during installation of the cable. Although theresults between the ribbon pullout force and the ribbon coupling forcemay have forces in the same general range, the ribbon coupling force isgenerally a better indicator of actual cable performance.

Specifically, the ribbon coupling test simulates an underground cableinstallation in a duct by applying 600 pounds of tension on a 250 mlength of cable by placing pulling sheaves on the respective sheathes ofthe cable ends. Like the ribbon pullout test, this test is equallyapplicable to loose or bundled optical waveguides. However, othersuitable loads, lengths, and/or installation configurations can be usedfor characterizing waveguide coupling in other simulations. Then, theforce on the optical waveguide(s) along its length is measured from theend of cable. The force on the optical waveguide(s) is measured using aBrillouin Optical Time-Domain Reflectometer (BOTDR). Determining abest-fit slope of the curve normalizes the ribbon coupling force. Thus,according to the concepts of the present invention the coupling force ispreferably in the range of about 0.5 N/m to about 5.0 N/m, morepreferably, in the range of about 1 N/m to about 4 N/m. However, othersuitable ranges of coupling force may provide the desired performance.

Additionally, the concepts of the present invention can be employed withother configurations of the dry insert. As depicted in FIG. 7, dryinsert 74 has a first layer 74 a and a second layer 74 b that includesdifferent suitable types of water-swellable substances. In oneembodiment, two different water-swellable substances are disposed in, oron, second layer 14 b so that tube assembly 10 is useful for multipleenvironments and/or has improved water-blocking performance. Forinstance, second layer 14 b can include a first water-swellablecomponent 76 effective for ionized liquids such as saltwater and asecond water-swellable component 78 effective for non-ionized liquids.By way of example, first water-swellable material is a polyacrylamideand second water-swellable material is a polyacrylate superabsorbent.Moreover, first and second water-swellable components 76,78 can occupypredetermined sections of the water-swellable tape. By alternating thewater-swellable materials, the tape is useful for standard applications,salt-water applications, or both. Other variations of differentwater-swellable substances include having a water-swellable substancewith different swell speeds, gel strengths and/or adhesion with thetape.

FIG. 8 depicts another embodiment of the dry insert. Dry insert 84 isformed from three layers. Layers 84 a and 84 c are water-swellablelayers that sandwich a layer 84 b that is compressible for providing acoupling force to the at least one optical waveguide. Likewise, otherembodiments of the dry insert can include other variations such at leasttwo compressible layers sandwiching a water-swellable layer. The twocompressible layers can have different spring constants for tailoringthe normal force applied to the at least optical waveguide.

FIG. 9 illustrates a dry insert 94 having layers 94 a and 94 b accordingto another embodiment of the present invention. Layer 94 a is formedfrom a closed-cell foam having at least one perforation 95 therethroughand layer 94 b includes at least one water-swellable substance; however,other suitable materials can be used for the compressible layer. Theclosed-cell foam acts as a passive water-blocking material that inhibitswater from migrating therealong and perforation 95 allows an activatedwater-swellable substance of layer 94 b to migrate radially inwardtowards the optical waveguide. Any suitable size, shape, and/or patternof perforation 95 that allows the activated water-swellable substance tomigrate radially inward to effectively block water is permissible. Thesize, shape, and/or pattern of perforations can be selected and arrangedabout the corner optical waveguides of the stack, thereby improvingcorner optical waveguide performance. For example, perforations 95 canprovide variation in dry insert compressibility, thereby tailoring thenormal force on the optical waveguides for maintaining opticalperformance.

FIG. 10 depicts dry insert 104, which illustrates other concepts of thepresent invention. Dry insert 104 includes layers 104 a and 104 b. Layer104 a is formed of a plurality of non-continuous compressible elementsthat are disposed on layer 104 b, which is a continuous water-swellablelayer. In one embodiment, the elements of layer 104 a are disposed atregular intervals that generally correlate with the lay length of aribbon stack. Additionally, the elements have a height h that variesacross their width w. Stated another way, the elements are shaped toconform to the shape of the optical waveguides they are intended togenerally surround.

FIG. 13 depicts cable 130, which is another embodiment of the presentinvention that employs tube assembly 10. Cable 130 includes a sheathsystem 137 about tube assembly 10 for protecting tube assembly 10 from,for instance, crushing forces and environmental effects. In this case,sheath system 137 includes a water-swellable tape 132 that is secured bya binder thread (not visible), a pair of ripcords 135, an armor tape136, and a jacket 138. Armor tape 136 is preferably rolled formed;however, other suitable manufacturing methods may be used. The pair ofripcords 135 are generally disposed about one-hundred and eighty degreesapart with about ninety degree intervals from the armor overlap, therebyinhibiting the shearing of ripcord on an edge of the armor tape duringuse. In preferred embodiments, ripcords suitable for ripping through anarmor tape have a construction as disclosed in U.S. patent applicationSer. No. 10/652,046 filed on Aug. 29, 2003, the disclosure of which isincorporated herein by reference. Armor tape 136 can be either adielectric or a metallic material. If a dielectric armor tape is usedthe cable may also include a metallic wire for locating the cable inburied applications. In other words, the metallic wire makes the cabletonable. Jacket 138 generally surrounds armor tape 136 and providesenvironmental protection to cable 130. Of course, other suitable sheathsystems may be used about the tube assembly.

FIG. 14 depicts fiber optic cable 140. Cable 140 includes at least oneoptical waveguide 12 and a dry insert 14 forming a cable core 141 withina sheath system 142. In other words, cable 140 is a tubeless designsince access to the cable core 141 is accomplished by solely cuttingopen sheath system 142. Sheath system 142 also includes strength members142 a embedded therein and disposed at about 180 degrees apart, therebyimparting a preferential bend to the cable. Of course, other sheathsystems configurations such as different types, quantities, and/orplacement of strength members 142 a are possible. Cable 140 may alsoinclude one or more ripcords 145 disposed between cable core 141 andsheath 142 for ripping sheath 142, thereby allowing the craftsman easyaccess to cable core 141.

FIG. 15 depicts a fiber optic cable 150 having a plurality of tubeassemblies 10 stranded about a central member 151. Specifically, tubeassemblies 10 along with a plurality of filler rods 153 are S-Z strandedabout central member 151 and are secured with one or more binder threads(not visible), thereby forming a stranded cable core. The stranded cablecore has a water-swellable tape 156 thereabout, which is secured with abinder thread (not visible) before jacket 158 is extruded thereover.Optionally, aramid fibers, other suitable strength members and/or waterblocking components such as water-swellable yarns may be stranded aboutcentral member 151, thereby forming a portion of the stranded cablecore. Likewise, water-swellable components such as a yarn or tape may beplaced around central member 151 for inhibiting water migration alongthe middle of cable 150. Other variations of cable 150 can include anarmor tape, an inner jacket, and/or different numbers of tubeassemblies.

FIGS. 19 and 20 depict explanatory tubeless cable designs according tothe present invention. Specifically, cable 190 is a drop cable having atleast one optical waveguide 12 generally surrounded by dry insert 14within a cavity of jacket 198. Cable 190 also includes at least onestrength member 194. Other tubeless drop cable configurations are alsopossible such as round or oval configurations. FIG. 20 depicts atubeless figure-eight drop cable 200 having a messenger section 202 anda carrier section 204 connected by a common jacket 208. Messengersection 202 includes a strength member 203 and carrier section 204includes a cavity having at least one optical waveguide 12 that isgenerally surrounded by dry insert 14. Carrier section 204 can alsoinclude at least one anti-buckling member 205 therein for inhibitingshrinkage when carrier section 204 is separated from messenger section202. Although, FIGS. 19 and 20 depict the dry insert of FIG. 2 a anysuitable dry insert may be used.

Many modifications and other embodiments of the present invention,within the scope of the appended claims, will become apparent to askilled artisan. For example, optical waveguides can be formed in avariety of ribbon stacks or configurations such as a stepped profile ofthe ribbon stack. Cables according to the present invention can alsoinclude more than one optical tube assembly stranded helically, ratherthan S-Z stranded configurations. Additionally, dry inserts of thepresent invention can be laminated together as shown or applied asindividual components. Therefore, it is to be understood that theinvention is not limited to the specific embodiments disclosed hereinand that modifications and other embodiments may be made within thescope of the appended claims. Although specific terms are employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation. The invention has been described withreference to silica-based optical waveguides, but the inventive conceptsof the present invention are applicable to other suitable opticalwaveguides and/or cable configurations.

1. A tubeless fiber optic cable having a longitudinal length,comprising: at least one optical waveguide; at least one dry insert, theat least one dry insert generally surrounding the at least one opticalwaveguide, wherein the at least one optical waveguide has a normalizedpull-out force between about 0.5 N/m and about 5.0 N/m; and a cablejacket, the cable jacket surrounding the at least one optical waveguideand the at least one dry insert.
 2. The tubeless fiber optic cable ofclaim 1, the at least one dry insert comprising a felt having a heightof about 0.5 mm or more and comprising at least one type ofnon-continuous filament.
 3. The tubeless fiber optic cable of claim 2,the at least one type of non-continuous filament comprising at least twodifferent types of non-continuous filaments.
 4. The tubeless fiber opticcable of claim 2, the at least one dry insert being continuous along thelongitudinal length of the cable.
 5. The tubeless fiber optic cable ofclaim 1, the at least one dry insert comprising at least two differenttypes of non-continuous filaments.
 6. The tubeless fiber optic cable ofclaim 1, the at least one dry insert comprising a plurality ofwater-swellable filaments.
 7. The tubeless fiber optic cable of claim 6,the plurality of water-swellable filaments comprising about 25% or less,by weight, of the dry insert.
 8. The tubeless fiber optic cable of claim7, wherein the plurality of water-swellable filaments comprise asuperabsorbent polymer.
 9. The tubeless fiber optic cable of claim 1,the at least one dry insert comprising a first layer and a second layer.10. The tubeless fiber optic cable of claim 1, the at least one dryinsert comprising a foam layer and a water-swellable layer.
 11. Thetubeless fiber optic cable of claim 10, the at least one dry insertbeing continuous along the longitudinal length of the cable.
 12. Thetubeless fiber optic cable of claim 1, further comprising at least onestrength member extending along the longitudinal length of the cable.13. The tubeless fiber optic cable of claim 1, further comprising atleast one ripcord.